Some explanation of Dennis's post, above: I asked him to change the name of the thread from "New Highlander Build" to "Sheepdog's Highlander Build", because, at 3 years old, it isn't exactly "New" any more. And I threatened to bribe him with a ride. Looks like we both win.

There was a thread in 2012 called "Watertight Hinge Cavities" (http://www.wingsforum.com/viewtopic.php?f=218&t=21984). I decided to take a run at sealing those flap and aileron openings, too. After a couple of failed methods, I found a system that works well and adds very little weight.

I put some parchment paper on the worktable and laid up two layers of fiberglass fabric and resin. A couple of hours later I had a 16” x 20” sheet of flat material. I cut strips of it (with scissors) to fit the bottoms of the openings, with slits cut so they fit around the hinges.

There were some openings where the nose rib was positioned too far from the slot, or there wasn’t a nose rib at all. For these, I cut fiberglass nose rib shapes from the sheet and trimmed them so they just fit inside the leading edge. Using the kit’s packing foam, I cut nearly-weightless spacers that held the pieces in place. There were still a few gaps, and I filled the larger ones with bits of glass fiber, and the smaller ones with bits of packing foam. Once I had several openings fitted, I mixed up a small batch of resin and bonded the pieces into the openings. After the next batch was done, I went back and checked for gaps and re-coated.

I tried to keep things smooth enough that they wouldn't be too hard to rough up for paint. Here are examples, shown after the second coat of resin, but before any sanding. The fabric plates look odd because I’d already zinc chromated them before deciding to seal the openings.

I’m a newbie at working with fiberglass, but this wasn't too hard to figure out. All the seals are strong and the openings are watertight.

One thing to note: positioning the seals is pretty easy on the flaps. But, on the ailerons, if the seals aren't low enough, they interfere with the full motion of the control surfaces. It’s particularly critical on the ends. When I went back for a fit check on the wings, I found that three of the six aileron seals (including the one in the first picture) were too high, and the ailerons were limited to 20 degrees up travel. Oops. I had to cut the offending seals out and place new strips, making sure they were as low as possible. Space is pretty tight in there, and a fit check is a good idea before adding resin.

The one good thing that came of that mistake was knowing the seals are in there solidly. I had to use a vibratory multi-tool to saw the mistakes out.

The fiberglass sheet is surprisingly light, and it doesn't take much resin to seal everything up. Seems like having dry flaps and ailerons is well worth the few ounces added.

By the way, these control surfaces still need drain holes so they don't turn into balloons in the sun.

If I were starting the control surfaces anew, I’d make some changes: (1) I'd be a lot more careful about cutting the slots in the leading edge. A couple of them were crooked, and they were tough to straighten out. (2) I’d put a fiberglass cap on the sides of each hinge slot to go with the fiberglass strip on the bottom, and then I’d resin-coat the entire slot. That would make each leading edge a single waterproof piece. (3) I’d make a smaller sheet of two-layer fiberglass; I used less than half of what I made. (4) I’d make some three-layer fiberglass and use it for at least some of the fabric plates, too. It’s lighter than the aluminum, easier to shape, and could just be bonded in place.

We don’t “need” a cargo door. But I wanted one for longer trips, for inspections (when I’d end up crawling into the cargo bay to get to the aft access panel), and as easy access to the towbar.

It's almost ready for cover:

Here’s the system opened up:

The opening extends from the top longeron down to just above the rudder cable. It’s about 25” wide at the top, 5” wide at the bottom, and a minimum of 19” high.

The structural integrity of the fuselage isn’t compromised. I did cut out a section of the (non-structural) side stringer between the spigots.

The doorframe is made from 1-½” x .060” 6061-T6 aluminum strips that I made into Z shapes with two 90-degree bends. These channels make a doorframe strong enough to lean on, and stiff enough to hold fabric through shrinking. They’re installed so the outer face is flush with the longerons and stringer. The inner blade of each channel holds the same seal material that I used on the cabin doors, McMaster-Carr part 12335A56, http://www.mcmaster.com/#bulb-seals/=mq36t8. Here’s how the seal looks installed on a piece of channel:

Cargo Door Z-angle and Seal 1s2.jpg (33.52 KiB) Viewed 4798 times

Upper channels run from the top longeron down to the stringer/spigot, and the lower channels run from the stringer/spigot to the bottom longeron. They form a V that meets at the junction of the vertical fuselage tubes.

A short piece of the Z-channel is fastened between the channel legs just above the rudder cable to add strength and to form the bottom of the doorframe. Just below the rudder cable, the lower legs are attached with Adel clamps to the vertical fuselage tubes. At the stringer/spigot joints, both top and bottom channels are epoxied and riveted in with small angle brackets of .030” aluminum.

Where the top channels meet the upper longeron, a ½” aluminum U-channel is installed, angled slightly so its outer edge parallels the slope of the fabric. It fits between the upper Z-channels and is epoxied to them and the longeron. The U-channel provides a place to rivet the upper hinge and the seal flange without drilling into the longeron.

Door skins are .030” aluminum, and the edges are reinforced with .030” aluminum Z-channel (¾”-½”-½”) riveted to them with 3/32” countersunk squeezed rivets (AN426A-3-4). The inner corners of the Z-angles are riveted together, which gives the doors the strength of three-dimension panels, but keeps them light. They’ll be covered with fabric.

The doors are hinged with the same aluminum piano hinge that’s used on the cabin doors. The door half of the hinge is flipped over so the door face is flush when closed, and will still open 180 degrees. It’s riveted between the door face and the Z-channel door reinforcement.

The entire opening is surrounded by the seal material, which keeps out the elements and cushions the opening when leaning into it. A strip of the seal material is also installed on a flange built into the top of the lower door, and the upper door closes against it. The ends of the seal flange also help guide the lower door to the proper position when closed, making up for the surprising amount of “wobble” allowed by the bottom piano hinge, which is less than 6” long.

The lower door is held closed by pivot latches that swing down behind the seal and keep ithe door flush with the fuselage. They’re made from 1/2” aluminum angle, 6-32 nutplates and 6-32 stainless steel machine screws with nylon washers to eliminate abrasion. Here’s one in the unlatched position:

… and here it is latched. The stop keeps it from vibrating open.

The upper door isn’t perfectly flat (because the top longeron is straight, and the stringer is curved), and the seal material pushes against the door, so it needs to be held flush with the fuselage at its bottom corners. The outward pressure is light enough that spring-loaded grab catches, McMaster-Carr 12855A12, can do the job well:

Cargo Door Catch 2s.jpg (5.26 KiB) Viewed 4798 times

One is mounted on a bracket at the rear of the upper door.

While another catch at the front of the door would work, catches aren’t positive locks, and there would be no way to ensure the door won’t pop open in flight. So, instead of that second latch, I installed a keyed cam lock at the front. It holds the door in and keeps opportunistic thieves out. The lock is weather-resistant, and uses the same key as the cabin door locks. To minimize the weight of the door itself, I mounted the lock in the aluminum window panel forward of the door.

Cargo Door Lock 1s2.jpg (40.66 KiB) Viewed 4798 times

The steel locking blade turns down into an aluminum angle strike plate mounted on the forward edge of the door:

Cargo Door Strike 1s2.jpg (27.02 KiB) Viewed 4798 times

The strike plate is angled so the blade draws the door in as it drops into place. The mounting holes are slots, and the 6-32 stainless steel screws are held by nutplates in the door reinforcement channel. I’ll mount an .060”-thick plastic rub strip to cushion the contact area. Here’s how it looks in action, from inside the plane:

Cargo Door Lock 3s2.jpg (34.35 KiB) Viewed 4798 times

I’ve sized the gaps around and between the doors for covering, but I’ll get the fuselage cover on, and then gauge how much -- if any -- I may need to trim the edges of the doors before covering them.

In the pictures, the upper door isn’t installed, yet -- it’s just clamped in place. The door and the top flange for the seal material will be riveted to the top channel after everything is covered. The seal material and the door portion of the grab catch will be installed after cover, too.

Yep, this system is heavier than just covering the area with fabric. I didn’t weigh the parts as I installed them, so I can’t provide a number. Being the first one I’ve built, I focused more on keeping it strong, rather than light. If I were to build it again, lighter gauge skin material would work, and I could reduce the dimensions on the door reinforcements. As long as there’s enough material to resist the forces of shrinking the cover material, I think the skin could be just a frame around the periphery of the door. I’m considering lightening holes to save a good bit of weight in these.

Well, not yet, anyway. While I don't expect any problems, this is not a flight-tested system. I'll want to see this prototype covered and flight-tested first. Then I'd like to explore some ways to reduce the weight.

Great workmanship. I like the positive key latch on the front end, I am curious though about the rear door catch. I wonder how it will behave with differing pressures along the fuselage. just concerned that perhaps it could pop the back half open in a turn or something as the pressure outside the fuselage skin drops and inside the cabin rises. I guess in my little pea brain, I would feel better about a positive latch fore and aft. But I like the simplicity of the latch...Im slowly catching up with work, and am excited to get back to my airplane, who knows, I might even find some time to update my website too...

Great workmanship. I like the positive key latch on the front end, I am curious though about the rear door catch. I wonder how it will behave with differing pressures along the fuselage. just concerned that perhaps it could pop the back half open in a turn or something as the pressure outside the fuselage skin drops and inside the cabin rises. I guess in my little pea brain, I would feel better about a positive latch fore and aft. But I like the simplicity of the latch...Im slowly catching up with work, and am excited to get back to my airplane, who knows, I might even find some time to update my website too...

That little grab catch is pretty strong, but it's still a question mark. It should withstand the small pressure that will be exerted. Even if it pops, the back bottom of the upper door would stick out only a little, but that wouldn't be acceptable. Before covering, I plan to epoxy in a small triangle of aluminum skin aft of that area in case flight testing shows that I need to add a second cam lock in place of the grab catch.

The door is done, though it isn't painted or covered, yet. Here's the final result:

I decided a second lock was just too much extra weight, so I took the lock out from in front of the door and filled in the hole. I replaced the lock with a second plastic catch, matching the one at the rear. The catches are strong... they hold the door so tightly that there’s no way to open it without a handle. So I formed a little tab that can be pulled easily. It’s riveted to the back of the door face and sits in a notch so it’s flush with the bottom of the door.

I moved the lock into the lower door, and then made a catch on the upper door for a the lock arm to swing up into. The heavy steel arm that came with the lock is now a much shorter and lighter arm I made from .090” 6061 T6. The usual way to install this would be with the lock in the upper door, but I wanted to keep that door as light as possible in case I have it open and a gust blows it closed onto my head. I figure a lighter door will result in a smaller scar.

A few tasks remain: cut lightening holes in both door skins, paint the doors with zinc chromate, and cover them.

This cargo door would have been easier to install if I’d just put a single door in the area above the stringer, or a single door below the stringer in the bay in front of its current location. Making two doors fit and work together took a good bit of extra time. But, now that it’s done, I’m enjoying it… it’s sure a lot easier to install the header tanks and the cargo area floor panels.

Our standard cabin doors are light, functional, and easy to install. But they don’t seal very well, and they’re certainly not the airplane’s best feature. I wanted doors that seal out the elements. I posted earlier that we were working on a system, but suggested it was too early to declare victory. Now, though, we have a flight-proven system.

I tried plenty of approaches that led to dead ends or were impractical to install before I found a solution: an “edge-grip” seal. It mounts on a flange epoxied to the doorframe tubing. Here’s the seal and one version of the seal mounts we built:

The system can be installed as the plane is built, or it can be fitted after covering and painted or powder coated before installation. It does slightly reduce the size of the door opening, so existing doors need modification.

Frame Components - Version 1I’d been talking with Scot Blankenship about ways to build the support system for the seal, and he’d contributed some really good ideas. His Highlander was already covered and painted, so we decided we should install the system on his plane and get him flying.

Scot’s system is based on aluminum extrusions with 1/16” wall, like the picture above. The 3/4” (inside dimension) channel fits down tightly over three sides of the 3/4” steel fuselage tubes that form the door opening, and squares off the surface of the doorframe. A 1/2” aluminum angle is solid-riveted to the channel, and that assembly is epoxied to the fuselage rails. Once the frame is installed, the edge-grip seal goes on the angle, all around the frame (except at the top).

Here’s a cross-section sketch of his system, with the door just barely open:

The C-channel is labeled 7/8", which is its outside dimension, but it's sold as 3/4" C-channel, referring to its inside dimension

The Lexan door material doesn’t lay against the fuselage fabric. Instead, it’s sized to fit just inside the channel so it rests only against the seal. The Lexan closes against the leaf of foam and presses it in. This seal is particularly good for this application, because air that might get under the door is trapped and simply pushes the seal tighter against the door, keeping out wind and weather. The base of the seal is hard rubber, and it protects humans from the “blade” it grips, so getting in and out is still comfortable. The seal also protects the bottom of the doorframe from feet.

On Scot’s plane, N982LT, we installed the C-channel first, and got all those parts to fit. Then we added the angle, and then made the door parts. We held the parts on with painter’s tape. In this picture, all the frame and door parts are installed (except the middle bar of the door), but no epoxying is done, yet:

The outer ring of silver is the seal mount; the inner ring is the square tubing door. The door is shimmed ⅜” away from the blade, resulting in about 1/4” gap between the door and the installed seal.

After Scot’s parts were fitted, he had them powder coated, and then epoxied the seal mounts in place. Here’s the finished product:

Scot has well over 300 hours on this door system, and he’s very happy with the result. He flies comfortably in winter weather.

Frame Components - Version 2After we got Scot’s parts finished, I kept refining and testing new designs to make the system lighter. For N7340Z, I built seal mounts from .032” 6061-T6 aluminum sheet, bent to form inner and outer components. The two parts are riveted together with countersunk 3/32” solid rivets (AN426A-3-3 or -4) to form a mount that clips down over the door tubes. The mount sections are epoxied in place, and they’re absolutely solid. Here’s a sketch of that system:

The outer component is a 1-1/2” strip bent 90 degrees twice to form two 1/2” flanges. The inner component has a 1/2” upper flange, and the other segments are 1/4” and 5/16” wide. It uses two 45-degree angles to reduce weight, and to make it easier to install interior materials.

Around the door, each mount section is separate. Here’s the lower part of the right side door opening with the mount sections in place, but not epoxied:

I put large rear windows in N7340Z, and built the window panels to be epoxied in place. I bent the forward edge of each window panel so it became the outer component of the seal mount:

I made a new Windshield Angle Bracket that incorporates the seal mount, but it would have been easier to simply rivet aluminum angle to the standard part. Either way, this section of the system doesn’t get epoxied in place:

On the SuperSTOL, the lower front door frame would need the added angle, too.

Here’s the back of the doorframe with the bead seal temporarily mounted:

You may notice that the doorstop blade between the two back tubes is gone. Troy confirmed that it’s non-structural, so I cut it out. On Scot’s already-covered plane, we didn’t cut it completely out, but we reduced the height so it wouldn’t interfere with the seal mount installation.

When covering, the fabric wraps over the outer component and can be stopped at the blade or it can run up onto the blade. Here’s N7340Z, covered, with the seal installed:

I’m still working on these… the seal mounts were completed, but I’m revising the cowl side panels, so I’ll be rebuilding those parts.

DoorsThe flange and seal shrink the door opening about 5/8”. It’s not a noticeable change in use, but it means that most of the door tubes must be slightly shorter. We both built doors from scratch, but existing doors could be made to fit by cutting a section out of each tube. The joints could be welded or patched with epoxied and riveted inserts. New Lexan would be necessary.

On N982LT, Scot’s doors are welded 3/4” square 6061 aluminum tubing. The center bar is ¾” round tube, and is bowed like the center bars in standard doors. The doors are strong, and a single latch pin at the front of the bottom bar easily holds them closed and sealed. Scot didn’t build separate windows in his doors.

For N7340Z, we built doors from ½” 6061-T6 tubing with welded joints, but I haven’t installed them. The SuperSTOL door “kits” would work well, too, and they eliminate welding. They consist of bent and welded steel fittings for the tube junctions, and aluminum tubes that are riveted (and optionally epoxied) onto them. Troy suggested gusseting the corners, and that’s a particularly good idea if epoxy isn’t used in the joints.

What About Windows?Neither Scot nor I put windows in our doors. I have a couple of ideas for adding windows, but that’s another development project -- a good winter project after we’re flying.

It’s Do-It-YourselfEither version will work on covered or not-yet-covered aircraft. We haven’t set up a kit system, because neither of us wants to be a manufacturer. If you want to build a system like this, I’d be happy to answer questions. I tried a whole lot of stuff, and I might be able to save you some trouble.

Scot’s system requires fewer tools, because we simply cut the extrusions to size and riveted the angle to the channel. The formed aluminum parts I used are thinner and lighter, but they take more fabrication time.

Neither of these systems is a weekend project. The major investment of time is in the details: getting the parts to fit so they meet perfectly at the corners. Some of the junctions are at odd angles, so there’s a lot of hand-filing to make them fit. We made several parts more than once. Doing a sample corner with some short pieces is instructional. Once you “get” the process, start with the long parts. If you goof, you can cut them down to make the shorter parts.

If you’re retrofitting, you can do all the fitting without taking your plane out of service. In fact, you could probably fly right up to the point where you revise the doors.

If your plane isn’t covered yet, perfect fit is less important because fabric and paint can cover a lot of sins. You still want to be sure to get a smooth top line so the seal can go on straight.

Alternative SystemsThe primary advantage of the systems shown here is that we know they work. Finding the functional seal was the real key, and knowing it works opens up a range of possibilities.

The seal specs call for a blade between 3/64" and 9/64" thick. Ours were built with processes I know, but other blade designs are certainly possible, and you may come up with something lighter, or easier, or less expensive.

A middle ground between these techniques might be to form an .032 C-channel that just fits on the fuselage tubes, and rivet a formed blade to it.

If welding is in your skillset, a blade of .032” 4130 steel could be welded to the doorframe tubes, and just the outer component of formed aluminum or fiberglass could be attached to it. I’d start with some tabs and see if that’s all that would be necessary.

If fiberglass is in your comfort zone, perhaps the outer component could be made of preformed fiberglass, and that shape could simply be glassed onto the tubes.

Come and VisitWe’re both happy with the systems we have. If you want to see them up close, check with Scot at the factory and arrange to see N982LT. If you get to Atlanta, N7340Z and I are less than an hour drive west of Atlanta International Airport.

The two-for-one option is to be at the the Just Plane Fun Fly-In in Brasstown, NC. I may not have N7340Z flying yet, but I do expect to have her up there, and Scot’s there every year with N982LT.

Raw MaterialsThe seal we used is McMaster-Carr part 12335A56, http://www.mcmaster.com/#12335a56. We needed about 17 feet of it to go around both doors. I’m exploring adding the seal across the top of the door, and that will make the total requirement 22 feet.

The aluminum seal mount parts aren’t structural, so hardware store aluminum extrusions work. The C-channel is 3/4” x 9/16” x 1/16” (Home Depot Model# 802667, SKU 797138, http://www.homedepot.com/p/204274001?keyword=802667). The angle is standard 1/2” x 1/2” x 1/16” aluminum (Home Depot #800047, http://www.homedepot.com/p/204604756?keyword=800047). These extrusions come in 8-foot lengths. They’re currently shipping free with a $45 order, and three of each should give you enough material with some extra for mistakes, and will make it over the free shipping mark.

I used AN426-3-4 countersunk head solid rivets on the aluminum extrusions, and AN426-3-3 on the .032 parts. If you order the rivets from Aircraft Spruce, an ounce -- 250 to 300 rivets -- is plenty.

I used Richards second method and it works very well although I haven't flown with it. The only problem I had with it is the aft upper part of the door the clearance will not allow the thicker seal but the seal supplied with the super stol for the slats seems to work well for aft upper section and the recommeced seal for the rest of the door.Wayne

Sheepdog, that is one heck of a post. When can we expect to see the fully detailed and illustrated build manual with tricks and tips? It would be a huge hit! Very nice work. I consider the door assembly the weakest part of the Highlander and I have though quite a bit about how to improve it. Your details are quite simple excluding the modifications that would be necessary to the door itself. Looks like your modification improves the seal as well as improving the drag. Did you happen to weigh the parts before assembling them for a total weight increase on both aircraft? Great post. Joe B